/*
 * Copyright (c) 2018, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "StdAfx.h"
#include <time.h>

#ifndef ACL_PREPARE_COMPILE
#include "stdlib/acl_define.h"
#include "thread/acl_pthread.h"
#include "stdlib/acl_timeops.h"
#endif

/* This is a safe version of localtime() which contains no locks and is
 * fork() friendly. Even the _r version of localtime() cannot be used safely
 * in Redis. Another thread may be calling localtime() while the main thread
 * forks(). Later when the child process calls localtime() again, for instance
 * in order to log something to the Redis log, it may deadlock: in the copy
 * of the address space of the forked process the lock will never be released.
 *
 * This function takes the timezone 'tz' as argument, and the 'dst' flag is
 * used to check if daylight saving time is currently in effect. The caller
 * of this function should obtain such information calling tzset() ASAP in the
 * main() function to obtain the timezone offset from the 'timezone' global
 * variable. To obtain the daylight information, if it is currently active or not,
 * one trick is to call localtime() in main() ASAP as well, and get the
 * information from the tm_isdst field of the tm structure. However the daylight
 * time may switch in the future for long running processes, so this information
 * should be refreshed at safe times.
 *
 * Note that this function does not work for dates < 1/1/1970, it is solely
 * designed to work with what time(NULL) may return, and to support Redis
 * logging of the dates, it's not really a complete implementation.
 */

#if defined(ACL_UNIX)

static int is_leap_year(time_t year) {
	if (year % 4) {
		return 0;         /* A year not divisible by 4 is not leap. */
	} else if (year % 100) {
		return 1;         /* If div by 4 and not 100 is surely leap. */
	} else if (year % 400) {
		return 0;         /* If div by 100 *and* not by 400 is not leap. */
	} else {
		return 1;         /* If div by 100 and 400 is leap. */
	}
}

static void nolocks_localtime(struct tm *tmp, time_t t, time_t tz, int dst)
{
	const time_t secs_min  = 60;
	const time_t secs_hour = 3600;
	const time_t secs_day  = 3600*24;

	t -= tz;                            /* Adjust for timezone. */
	t += 3600 * dst;                   /* Adjust for daylight time. */
	time_t days = t / secs_day;         /* Days passed since epoch. */
	time_t seconds = t % secs_day;      /* Remaining seconds. */

	tmp->tm_isdst = dst;
	tmp->tm_hour = (int) (seconds / secs_hour);
	tmp->tm_min = (seconds % secs_hour) / secs_min;
	tmp->tm_sec = (seconds % secs_hour) % secs_min;

	/* 1/1/1970 was a Thursday, that is, day 4 from the POV of the tm
	 * structure where sunday = 0, so to calculate the day of the week
	 * we have to add 4 
	 * and take the modulo by 7.
	 */
	tmp->tm_wday = (days + 4) % 7;

	/* Calculate the current year. */
	tmp->tm_year = 1970;
	while(1) {
		/* Leap years have one day more. */
		time_t days_this_year = 365 + is_leap_year(tmp->tm_year);
		if (days_this_year > days) {
			break;
		}
		days -= days_this_year;
		tmp->tm_year++;
	}

	tmp->tm_yday = (int) days;  /* Number of day of the current year. */

	/* We need to calculate in which month and day of the month we are.
	 * To do so we need to skip days according to how many days there are
	 * in each month, and adjust for the leap year that has one more day
	 * in February.
	 */
	int mdays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	mdays[1] += is_leap_year(tmp->tm_year);

	tmp->tm_mon = 0;
	while(days >= mdays[tmp->tm_mon]) {
		days -= mdays[tmp->tm_mon];
		tmp->tm_mon++;
	}

	tmp->tm_mday = (int) days + 1;  /* Add 1 since our 'days' is zero-based. */
	tmp->tm_year -= 1900;     /* Surprisingly tm_year is year-1900. */
}

static int daylight_active;

static void timezone_init(void)
{
	struct tm *aux;
	time_t t;

	/* Obtain timezone and daylight info. */

	tzset(); /* Now 'timezome' global is populated. */
	t = time(NULL);
	aux = localtime(&t);
	daylight_active = aux->tm_isdst;
}

static acl_pthread_once_t once_control = ACL_PTHREAD_ONCE_INIT;

struct tm *acl_localtime_r(const time_t *t, struct tm *result)
{
	if (acl_pthread_once(&once_control, timezone_init) != 0) {
		abort();
	}
	nolocks_localtime(result, *t, timezone, daylight_active);
	return result;
}

#elif defined(ACL_WINDOWS)

struct tm *acl_localtime_r(const time_t *t, struct tm *result)
{
# if _MSC_VER >= 1500
	if (localtime_s(result, t) != 0) {
		return NULL;
	}
	return result;
# else
	struct tm *p = localtime(t);
	if (p == NULL) {
		return NULL;
	} else if (result) {
		memcpy(result, p, sizeof(struct tm));
		return result;
	} else {
		return p;
	}
# endif
}

#else

struct tm *acl_localtime_r(const time_t *t, struct tm *result)
{
	return localtime_r(t, result);
}

#endif
